Sports Injury Prevention Research Group

The objective was to determine estrogen's influence on control of a skeletal muscle through measurements of motorneuron excitability (H:M ratio) and presynaptic inhibition (PI). Estrogen serum concentrations were measured at menses and ovulation of female subjects and compared to male controls. Data was analyzed from 12 females and 13 males reporting no history of knee ligament injury. Females reported regular menstrual cycles and no hormone-based contraceptive use for the previous year. Females were tested at menses (Time1) and ovulation (Time2). Males were tested twice, approximately 14 days apart. Analysis indicated no difference in the H:M ratio between the sexes at either time point. A significant difference for the sexes was detected in the magnitude of estrogen change (∆EST) between observations. At Time1 the male and female estrogen concentrations were not different, however they were different at Time2, primarily due to the large rise observed in the females. A significant difference between the sexes was also see in the magnitude of change for PI (∆PI) between observations. As with EST, the levels of PI between the sexes at Time1 were not different, however a difference existed at Time 2. Estrogen interacts with GABA at several nervous system locations affecting inhibition of synaptic transmission. This is the first study to investigate changes in PI of a skeletal muscle between times of low and high estrogen. Improving the understanding of estrogen's influence on skeletal muscles may provide answers to why non-contact anterior cruciate ligament injuries of the knee occur more frequently in females. This article is protected by copyright. All rights reserved.